The present invention relates to a process for manufacturing a composite assembly of the type including a ceramic inner member and an outer shell member fit around the inner member, wherein the outer shell member is heated and expanded, the members are mutually located at predetermined positions relative to each other, and the members are cooled such that the outer shell member shrinks onto the inner member, thereby forming the composite assembly.
This type of process is described in German DE 35 27 793, involving the manufacture of a gas flushing or purging stone or brick. In this known arrangement, a steel sleeve is heated by means of a flame or in a heating furnace. When heating the steel sleeve by a flame, the heating of the sleeve is nonuniform with the result that some areas of the sleeve remain colder than other areas thereof. The result is that the steel sleeve expands unevenly. Such differential expansion is disadvantageous during subsequent shrinking of the steel sleeve onto the ceramic stone or brick. When the outer sleeve or shell and the inner ceramic stone or brick are joined together, a process that is itself difficult due to the high temperatures involved and the necessary low tolerances of the dimensions of the two members, the outer shell or sleeve cools faster at outer edges thereof. As a result, shrinkage is not uniform. The same basic problems occur when the outer shell or sleeve is heated in a heating furnace.
Additionally, the heated steel sleeve or shell normally is grasped by pliers or tongs or the like and is moved thereby to the inner ceramic brick or stone and is positioned thereover. Those areas of the heated steel sleeve or shell that are grasped by such pliers or tongs are cooled more rapidly than the other areas of the heated steel sleeve or shell. As a result, when the heated steel sleeve or shell finally is positioned on the inner ceramic brick or stone, the expansion of the sleeve or steel further will be nonuniform. A further disadvantage of this arrangement is that the use of pliers or tongs to grip the heated steel sleeve or shell can result in deformation thereof. A further disadvantage of this known process is that inevitably the heated steel sleeve or shell loses significant heat due to radiation before final positioning with respect to the inner ceramic stone or brick. This requires initial heating to a higher temperature, and this is not economical.
German DE 35 38 421 also discloses another known process for assembling a gas flushing or purging stone or brick. In this arrangement a layer of refractory paper-like material is inserted between the brick and the steel sleeve. Such paper-like material can be formed of ceramic fibers and is intended to prevent unwanted passage of gas that can remain during the process of shrinking the outer shell or sleeve onto the inner ceramic member.